Chlorophyll Content. 87 



WiHstatter, however, expresses this opinion in a far more 

 dogmatic way, postulating that the chloroplast is the seat of a photo- 

 chemical reaction and that the product formed in this reaction is 

 subjected to an enzymatic action which takes place at the boundary 

 between chloroplast and plasma. In this latter process oxygen is 

 supposed to be evolved. His contention is that the efficiency of the 

 assimilatory process depends not only on the amount of chlorophyll 

 but also on the amount of enzyme, and in his investigation he has 

 examined extreme cases where either chlorophyll or enzyme are in 

 excess. 



The very great importance of Willstatter's work lies in the fact 

 that for the first time quantitative estimations of the pigments have 

 been made ; in an earlier chapter we have stated in some detail the 

 methods employed by WiHstatter and also pointed out how unreliable 

 were the estimations of all of the earlier workers. The principle 

 used in the analysis is the saponification of the leaf extract with 

 alkali and the subsequent abstraction of the yellow pigment with 

 ether. The chlorophyllin solution is then compared colorimetrically 

 with standard solutions. Thus the disturbing influence of the 

 yellow pigments is avoided; however, it must be pointed out that 

 the information obtained only holds for the chromogen complex ; 

 as regards the phytol part of the chlorophyll molecule which is 

 split off in the saponification we do not get any information. 



Willstatter's experience from earlier investigations wheie the 

 pigments were estimated in leaves collected at various times of the 

 day and at various seasons led him to the conclusions that the 

 amount of pigment is not altered during the processes of assimilation ; 

 this view is confirmed here, for WiHstatter finds no appreciable 

 difference in the amount of pigments as the result of assimilation. 



Of course it has been assumed before Willstatter's time that 

 the assimilation varies with the amount of chlorophyll, but it had 

 not been possible definitely to estimate the chlorophyll content or 

 to differentiate between the part played by the chlorophyll and the 

 part played by the plasma. 



Thus, for instance, Weber (1879) found that equal ai'eas of the 

 leaves of dnferent plants under the same conditions had different 

 assimilatory powers. Haberlandt (1882, and see 1914) explained 

 Weber's results by determining the number of cliloroplasts per 

 unit area in the plants used by Weber and showing that there is a 

 parallelism between the assimilatory activity and the number of 

 chloroplasts. His results are exhibited in the following table. 



